The invention relates to an active chassis system of a vehicle, in particular a passenger vehicle having two axles with two wheels each, whereby each vehicle wheel is supported on the vehicle body via a spring element and a hydraulic piston-cylinder unit acting as a damper and as a hydraulic actuator. The hydraulic piston-cylinder unit serves to introduce an additional force between the wheel and the body, whereby a hydraulic supply line is assigned to each of the working chambers of the actuator provided in the cylinder of the piston-cylinder unit on both sides of the piston, their cross-sectional areas differing from one another, such that these hydraulic supply lines serve to supply the respective working chamber with hydraulic pressure provided by a delivery pump via the respective working chamber. The working chambers of two actuators of one vehicle axle are connected hydraulically directly to one another with the smaller cross-sectional area in each case, and a directional valve is used for the roll control mode of operation.
Reference is made to German Patent Application DE 101 11 551 A1 for the known state of the art.
An active chassis system according to the present invention is fundamentally characterized by many degrees of freedom with regard to controllability, in particular also the positioning of the vehicle body with respect to the vehicle wheels. As indicated in German Patent Application 101 11 551 A1 cited above, an essentially known so-called roll stabilization as well as a level regulation of the vehicle body can then be implemented. It is advantageous from an energy standpoint if a spring element is connected in parallel with each actuator.
The object of the present invention is to provide an active chassis system which has a simpler design with improved function and is inexpensive to manufacture.
The object is achieved according to this invention with the features of claim 1. Additional embodiments of the invention are derived from the dependent claims.
According to this invention, an active chassis system of a vehicle, in particular a passenger vehicle having two axles with two wheels each, where each vehicle wheel is supported on the vehicle body via a spring element and a hydraulic piston-cylinder unit functioning as an actuator, and a hydraulic supply line is assigned to the working chambers of each actuator provided on both sides of the piston in the cylinder of the piston-cylinder unit, their cross-sectional areas differing from one another, the respective working chamber being supplied with hydraulic pressure provided by a delivery pump via the hydraulic supply line, whereby the working chambers of two actuators of a vehicle axle with the smaller cross-sectional area in each case are hydraulically connected directly to one another, and a directional valve is used for the roll control mode of operation, characterized in that the directional valve is a pilot-operated directional valve whose control pressure is tapped in parallel with a controllable throttle which is connected hydraulically between the two working chambers having the larger cross-sectional area of the two actuators of a vehicle axle and by means of which a pressure drop between the working chambers, which depends on the direction of rotation and/or the delivery output of the delivery pump, is adjustable.
This is a simple system that is inexpensive to manufacture and allows both roll control and level control as well as damping of lifting vibrations with a few components in a hydraulic circuit having a simple design. Flow can pass through the controllable throttle in two different directions, which has the effect that in comparison with the state of the art, the delivery pump can also be shut down if there is no transverse acceleration, e.g., when driving straight ahead. The controllable throttle has a good interference behavior with degressive characterization because pressure fluctuations are minimized. In addition, with a good design of the engine characteristics map and regulation of the throttle, the operating point of the delivery pump can always be kept at the nominal power. In the event of failure of the system, with no power, the front axle advantageously has a hard adjustment and the rear axle has a soft adjustment. The pilot-operated directional valve advantageously has a good response characteristic. The effect of using pilot operation is that no technical regulating complexity is required to switch the directional valve. The position of the directional valve is determined by the pressure drop on the controllable throttle, which in turn depends on the direction of rotation and the volume flow through the delivery pump, in addition to being induced by the resistance of the controllable throttle and the volume flow which is induced by rolling.
An advantageous embodiment of the invention is characterized in that the directional valve for roll control switches to one of its two end positions, while ensuring free spring deflection and rebound of the individual wheels in its middle position by means of an H circuit that equalizes the pressure between the four working chambers of the actuators of a vehicle axle. It is advantageous here if the directional valve is a 4/3-way valve or a 4/2-way valve, in particular with the end position.
A preferred embodiment of the invention is characterized in that the delivery pump withdraws the hydraulic medium for the level control operating mode from a tank or operates in a closed circuit for the roll damping operating mode and the mode of damping of lifting vibrations, said closed circuit having an equalizing volume, whereby a 3/2-way valve is connected to the hydraulic circuit, acting as the reversing valve between the closed circuit and the tank withdrawal in parallel with the controllable throttle and in series with the delivery pump.
It has been recognized that the entire hydraulic system can be “prestressed” so to speak for a cohesive operating time by connecting a hydraulic line, which functions more or less as the return flow line with respect to the working chamber of an actuator that is acted upon by a lower hydraulic pressure, to the intake side of the delivery pump. The hydraulic medium, which already has a certain pressure level (and is no longer pressureless as it comes from the tank) is thus made available to the delivery pump at the intake end, thereby reducing the pressure difference that must be generated by the delivery pump for supplying the desired maximum pressure.
Presupposing an adequate imperviousness of the hydraulic system, there is a return flow of hydraulic medium into a hydraulic tank with a hydraulic circuit like that described so far practically only when the vehicle body is to be lowered, i.e., its level is to be reduced or when the load on the vehicle body is to be reduced. Apart from special boundary conditions or operating conditions, the delivery pump need only deliver enough hydraulic medium (in addition) from a tank (such as the aforementioned tank) into the hydraulic circuit of the active chassis system—assuming an adequate imperviousness of the system as a whole—until reaching the desired level of the vehicle body with respect to the vehicle. wheels and ensuring a sufficiently high hydraulic pressure in the system. Then the 3/2- way valve connected in series with the delivery pump can be switched, after which the delivery pump operates in a closed hydraulic circuit, uncoupled from the hydraulic tank.
In addition, in the active chassis system, an equalizing volume may also be provided as a pressure accumulator, among other reasons so as to prevent cavitation phenomena in the hydraulic system. If, depending on the position of the directional valve in roll control, at least one of the working chambers of the actuators having the larger cross-sectional area is connected to the pressure accumulator that is acted upon with a certain minimum pressure, then the cavitation phenomena in the actuator working chambers can be prevented for all relevant forms of excitation. The pressure accumulator here preferably receives the hydraulic medium from the (adjustment) throttle outlet of the low-pressure side because the pressure level prevailing here is adequate with the prestressed hydraulic system according to this invention, i.e., when the (adjustment) throttle outlet of the low-pressure side is connected to the intake side of the delivery pump (and not to the tank for the hydraulic medium).
Such an equalizing volume, however, also has other advantages, e.g., for a passenger vehicle having two axles each having two wheels. First, the entire hydraulic system can be definitely improved, i.e., “prestressed” in this way so that the delivery pump then need provide only a sufficient hydraulic pressure to perform a roll stabilization. Furthermore, the equalizing volume may function as an intermediate buffer in the case of bilateral spring support of the vehicle body so a relatively soft lift spring rate can easily be achieved-if desired. Finally, such an equalizing volume is also helpful to achieve an essentially constant vibration-inherent frequency of the vehicle body regardless of different loads and thus varying weights of the body. A so-called minimal pressure in the hydraulic system and thus also in the pressure accumulator can thus be established and thus also it can be established in the pressure memory device that the vibration-inherent frequency of the vehicle body is essentially independent of the respective weight of the body.
Therefore, according to an advantageous embodiment of the invention, the equalizing volume is designed as a pressure accumulator and minimal pressure in the pressure accumulator is adjusted so that the vibration-inherent frequency of the vehicle body is essentially unchanged with different weights of the body, in particular resulting from a different load on the body.
For spring deflection on both sides, an especially advantageous embodiment of the invention is characterized in that a 4/2- way valve is connected in series as the lifting valve between the directional valve and the hydraulic supply line of the working chambers of the actuators with the smaller cross-sectional area and/or equalizing volumes, said lifting valve supporting the lifting vibrations and a nonreturn valve that blocks the flow for the directional valve is connected in parallel for its passage to the hydraulic supply line of the working chambers, and for its passage to the equalizing volume, another valve return valve that blocks the flow thereto is connected in parallel.
According to another preferred embodiment of the invention, each working chamber of an actuator is connected in series to the respective hydraulic supply line via a throttle or an adjusting throttle, whereby this is bridged in parallel by a nonreturn valve that blocks the passage in the direction of the supply line.
Thus it is possible to prevent cavitation phenomena, in particular in the working chambers which are constantly exposed to the higher hydraulic pressure and which have a smaller cross-sectional area than the other actuator working chambers, even with extreme piston movements (i.e., with high rates of spring deflection and rebound of the active chassis system). This increases the functional reliability and the perceptible driving comfort of the active hydraulic chassis system.
According to additional advantageous embodiments of the invention, at least the directional valve and the controllable throttle are combined to form a first joint valve block. In addition, this valve block may also include the lifting valve with its nonreturn valves if necessary. A second valve block may then advantageously comprise at least the reversing valve, the delivery pump and its drive.
An active chassis system for both axles, e.g., of a passenger vehicle having a simpler design with improved function and being more economically manufacturable can then be characterized advantageously in that it comprises a first valve block for each axle, whereby a single second valve block is provided, comprising one reversing valve and one delivery pump per axle, and the drive for all the delivery pumps is provided by a single drive motor.
When the flow channels and control edges of the directional valve are designed and positioned in relation to one another so that the opened flow-through area is constant at least at the valve inlet, this also has the advantage that operation of the directional valve does not affect driving comfort because the total flow cross section remains constant regardless of the position while the final position damping of the directional valve ensures better acoustics.
Two preferred exemplary embodiments of the invention are depicted in greater detail in the following description and in the respective drawing. The same reference numerals are used for the same elements in the figures.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.